Which of the following statements about UNIX signals is NOT correct?

Explanation

SIGINT (statement 1), SIGTERM (statement 2) and SIGQUIT (statement 3) are all accurately described — these are ordinary, catchable and blockable termination-request signals that a process may trap and handle. SIGKILL, however, is deliberately designed so that it can never be blocked, caught, or ignored by any process; it is handled directly by the kernel and unconditionally terminates the target, which is exactly why it is used as the last-resort way to kill an unresponsive process. Calling SIGKILL "blockable" is therefore false, making statement (iv) the incorrect one.